The invention relates to an arrangement and a method for controlling a transmission in a motor vehicle. The transmission is continuously adjustable with respect, to its transmission ratio.
In a motor vehicles having a known continuously variable transmission (CVT) with a continuous element (for example, a thrust element belt or chain), the contact engaging force of the conical pulleys against the thrust element belt must be so adjusted via suitable measures that the torque, which is to be transmitted, can be transmitted. A high slippage between the continuous element and the pulleys occurs when the contact engaging force is too low and this can lead to damage. If the contact engaging force is, however, greater than absolutely necessary to avoid slippage, then the efficiency of the transmission drops which leads to an unnecessarily high consumption of fuel. For this reason, it is advantageous to so select the contact engaging force that the maximum tranmissible torque for this contact engaging force is only slightly greater than the torque to be transmitted at the particular time. If a high slippage of the continuous element nonetheless occurs, then measures must be taken in order to stabilize or stop the relative movement of the continuous element so that damage is avoided.
Conventional continuously variable transmission controls, such as disclosed in EP,A1,0 451 887, determine the transmission input torque from the torque, which is outputted by the engine, and the converter amplification. A belt tension is computed from this torque from which belt tension a contact engaging force results which makes possible a reliable transmission of this torque. Here, as a rule, a considerable reserve of reliability is considered which causes a higher fuel consumption. If an impermissibly high slippage nonetheless occurs, then, in general, the contact engaging force and therefore the belt tension is increased. The speed with which a reaction can be had to excessive slippage is, however, limited by the time constants of the hydraulic and of the mechanical system of the belt tensioning adjustment.
A system is known from EP,B1,0 446 497 (corresponding to US 5,098,345) for protecting against exceeding a maximum slippage of the belt. Here, a clutch is so controlled that this clutch always starts slipping at lower drive torques than the band. A reaction to a possible slippage of the band is not described here.
The detection of belt slippage is known in many configurations. Thus, and for example in accordance with U.S. Pat. No. 5,871,411, it is suggested to detect the speed of the continuous element. Furthermore, the belt slippage can be detected by a sensor which simulatneously detects the axial displacement of a conical-pulley pair and the rpm of this pair. From earlier German patent application 196 38 277.7, it is known to provide at least two sensor units for slippage detection which are mounted in the region of the continuous means and between the drive end and the output end.
The object of the present invention is to provide effective measures for excessive slippage in order to reliably avoid damage to the transmission.
As mentioned, the invention proceeds from a control of a transmission, which is continuously adjustable with respect to its transmission ratio, for a motor vehicle. The transmission is mounted in the drive train of the motor vehicle together with a drive unit having an adjustable drive torque. The transmission has a drive end and an output end and operative means for establishing a mechanical operative connection between the drive end and the output end. Furthermore, detecting means for detecting a slippage quantity is provided which represents the slippage between the operative means and the drive end and/or output end. Pregivable measures are initiated in response to a pregivable value of the slip quantity. The essence of the invention is seen in that the following are provided as measures:
a control of a clutch mounted in the drive train; and/or,
a change of the transmission ratio; and/or,
a change of the output torque of the drive unit.
It is especially intended here that the measures are initiated in the sense of avoiding slip.
In an advantageous embodiment of the invention, a further measure is a change of the contact engaging force between the drive end and/or the output end and the operative means, especially in the sense of avoiding slip.
The present invention describes how through slipping of the continuous element can be stopped and stabilized to a tolerable slip with three or four possible interventions when through slip of the continuous element is detected. The invention offers the possibility to undertake the introduced measures individually or with a coordinated strategy. Depending upon the particular situation, which led to a through slip of the continuous element, a response is provided in accordance with a previously determined strategy having a selection of the measures according to the invention simultaneously or in a tight time-dependent sequence. This always takes place with the objective to suppress a detected slip as quickly as possible and not to confuse the driver with effects of the measures. Depending upon the equipped variation of the vehicle, it is possible that not all of these measures can be carried out.
It is especially provided that:
the drive of the clutch takes place in the sense of an opening of the clutch; and/or,
the change of the transmission ratio takes place in response to a positive slip quantity in the sense of an increase of the transmission ratio and in response to a negative slip quantity in the sense of a reduction of the transmission ratio; and/or,
the change of the output torque of the drive unit takes placein response to a positive slip quantity in the sense of a reduction of the output torque and in response to a negative slip quantity in the sense of an increase of the output torque.
Furthermore, it is especially advantageous that the following is dependent upon the extent of the detected slip quantity:
the extent of the drive of the clutch; and/or,
the extent of the change of the transmission ratio; and/or,
the extent of the change of the output torque of the drive unit; and/or,
the extent of the change of the contact engaging force.
In a further advantageous embodiment of the invention it is provided that, simultaneously or in time after the drive of the clutch in the sense of an opening of the clutch, the following is provided: a change of the transmission ratio; and/or, a change of the instantaneous output torque of the drive unit; and/or, a change of the contact engaging force in such a manner that the maximum transmissible torque by the transmission becomes again greater in magnitude than the magnitude of the instantaneous output torque of the drive unit. In this way, the clutch slip can again be reduced by an increase of the maximum transmissible torque of the clutch (closing of the clutch).
It is especially provided that the change of the output torque of the drive unit for slip reduction is actuated as support to at least one of the other measures (clutch drive and/or change of the transmission ratio and/or contact engaging force).
As already described, the transmission can be a continuous transmission. The drive end and/or the output end can have at least an axially displaceable element which has essentially the form of a conical pulley. As operative means, at least a belt (preferably a thrust element belt) or a belt or a chain is tensioned between pulley pairs which define the drive end and the output end.